Sunday, January 13, 2008

Western Blue-tongued Lizard, Tiliqua occipitalis

Australia's largest skinks, subfamily Tiliquinae or the Egernia Group

There are two genera (Egernia and Tiliqua) represented in Australia from the subfamily Tiliquinae, which include the largest skink species. However DNA research has indicated a more complex relationship resulting in new groupings of related skinks, of which Egernia and Tiliqua have been placed with the genus Cyclodomorphus to form the Egernia Group, all of which are represented in Australia. These skinks can grow to over half a metre in length (including the tail), some are highly sociable and all bear live young.

The ancestors of these skinks are thought to have originated in Africa sometime after the demise of the dinosaurs and gradually migrated to various parts of the world, eventually arriving in Australia during the Pliocene (1.6 to 5.3 million years ago), via multiple colonisations from Southeast Asia. Since then they have evolved to around 40 odd indigenous species, the most from Egernia (currently 28 species), Tiliqua 6 species and Cyclodomorphus 9 species.

Skinks in the genus Tiliqua are known as 'Blue-tongue' lizards as all have a large flat blue tongue that is not only used to discourage predators, but also to scent prey.

I have already written about one Tiliqua species, T. rugosa (see item 10. Stumpy-tail Lizard ), which is very common in the Esperance region. Tiliqua occipitalis, the Western Blue-tongued Lizard is the only other Esperance (Western Australia) member of this genus, and is far less common, particularly in the sandy heath zones (the most common habitat in the Esperance region). This blue-tongue is more common around granite outcrops, probably reflecting its preferred habitat providing shelter under rocks from feral cats and foxes, both known to take a heavy toll on local wildlife. However if they manage to survive, they can live 20 to 30 years.

A female Western Blue-tongued Lizard, Tiliqua occipitalis

In the southeastern States (SA, Vic, NSW & southern Qld), there is a similar Blue-tongue Lizard naturally called the Eastern Blue-tongue or Common Blue-tongue Lizard. This skink grows to a similar size as its western cousin, but differs in several respects. The first noticeable feature is the general coloration; the western has a yellowish/brown overall look, whereas the eastern is more silvery grey. The bands on the body and tail also differ, with 4-6 DARK bands on the body (nape to hips) for the western, as against 6-9 PALE body bands for the eastern. There are 3-4 encircling dark bands on the western blue-tongue's tail, whereas the eastern has 7-10 pale bands.

So the basic coloration and number of bands are the easiest way of telling these two species apart, although there can be considerable variation with the markings. Other differences involve the number of live young each species produce, with the eastern being the more prolific by producing up to 25 young, although around half that number would be the norm. The Western Blue-tongue by contrast only produce from 5-10 young, but they are larger at birth. Neither species devote much time to their offspring and the young usually disperse within a few days to lead independent lives.

Western Blue-tongued Lizard, note the overall brownish hue

There are differences between male and female blue-tongue lizards; most obvious is the size of the head! The male's head is much broader than the female, who usually also has a longer body and shorter limbs. The males are usually more aggressive, although both can put up a good display to deter predators. Besides a deep guttural hiss and a gaping pink mouth to reveal a flickering broad blue tongue, they (particularly the western species) can flatten themselves by spreading their ribs, which they then turn side on towards the predator to make them appear much larger.

A male Western Blue-tongued Lizard

It is commonly thought that all skinks shed their tail to distract a predator. However this is not the case with all the skinks from this group, T. rugosa, the Stumpy- tail Lizard, plus several Egernia species lack fracture planes in their vertebrae so are unable to do so. Other species in this group gradually lose their ability to discard their tails as they mature, but could do so when young.

The blue-tongue lizards have a very catholic diet eating soft plant matter, flowers and fruit, crunchy beetles and other insects, spiders, small lizards, even silly young birds who venture too close, in fact they will eat almost anything that is slow enough and will fit into its large mouth, this also includes garden snails which they are able to crush with their strong jaws, so placing fingers near their mouth is not a good idea. Their limitation regarding diet is governed by their small legs and large body, which apart from a short lunge, mean they are normally quite slow and usually only able to catch slower prey.

As a word of caution, if you are fortunate to have these skinks living in your garden, please do not use snail pellets as they will eat the dying slugs and snails and become poisoned themselves. Best to leave it to your blue-tongue lizards to control your slug/snail problem.

Always ready for the next meal

Western Blue-tongued Lizard, Tiliqua occipitalis

Besides cats, dogs and foxes; snakes and birds will take young lizards, plus I strongly suspect they were also on the aborigine's menu. On some of the less frequented rocky outcrops around Esperance, lizard traps can still be found, these would have been used to catch another very large skink (as big or bigger than the western blue-tongue), Egernia kingii or the King's Skink that looks a little like a goanna. It has longer legs than Blue-tongue Skinks and can run very fast (been clocked at over 3 metres a second), so difficult to catch. However a large granite slab could be dropped on them simply by removing the supporting rock (see photo below). Therefore not only could these traps be used to catch these fast skinks, but the elevated slab would also provide good accommodation for the slow moving blue-tongues, who could easily be captured by hand. So travelling bands of aborigines could camp near a rocky outcrop and likely catch an easy evening meal, resetting the trap upon leaving to entice another large lizard for capture when they return on another occasion.

An aboriginal lizard trap, about a metre long x half a metre wide. Some are larger and require two rocks to support the granite slab.

The Western Blue-tongue has an extensive distribution, from the WA mid west coast, the southern goldfields, over the boarder to occupy much of SA, even extending into the Northern Territory. This species is also found in western NSW, Qld and Victoria, although here they are becoming increasingly rare. It is primarily a lizard of arid regions and is not normally found in cool forests. Probably it is this more open, warmer and drier habitat preference that excludes it from the eastern species range, where forested areas are more extensive but are not a problem for the eastern blue-tongue providing the forested area is not too wet and sunlight can reach the forest floor.

This Western Blue-tongue is not being rude, just smelling the environment with its tongue

Blue-tongue lizards are quite common in most capital cities these days, possibly as there are fewer predators who wish to eat them, rather, most domestic animals are more curious and easily discouraged by their aggressive display. To attract them to your garden, place large logs, rocks and have plenty of ground cover in which they can shelter. Do not use snail pellets and watch out when mowing. Then besides a harmless, attractive, interesting and interactive garden resident, you also get a free creepy crawly and expert snail catcher to boot. Sounds like a good deal to me!

5 comments:

"Then besides a harmless, attractive, interesting and interactive garden resident, you also get a free creepy crawly and expert snail catcher to boot. Sounds like a good deal to me!"

Sounds like a good deal to me too, and as my ground-covers and native shrubs become established I hope to have Eastern Blue-tongue lizards visit my garden more regularly, and even take up residence.

An excellent blog, Jack, and a very useful description of the differences in eastern and western species, along with male and female. It always amuses me to see a blue-tongue lizard moving as if 'gliding', such is its slow and smooth movement. The legs just don't look sturdy enough to carry the bulky body.

Unfortunately, I see more blue-tongue lizards squashed on the road than I see alive and well. Dragon lizards are much easier to remove from harm's way when encountered sunbaking on the road, as one only has to chase them and they will scoot to the safety of roadside vegetation, but blue-tongues will turn and take up a defensive stance instead. So now I carry a pair of gloves in my car in case I have to pick one up to move to safety.

I will look forward to the time when you will feature the King Skink in your blog.

Oh, and you have captured the 'cheeky' lizard with the curled tongue display in an excellent portrait - it brought a smile to my face.

Thanks for your comments Gaye, we both seem to agree that reptiles are fascinating creatures. I think as Australia has so many reptile species (far outnumbering mammals) that everyone should have at least 6 species living in their garden. The way to do this is of course to provide suitable habitat for them, which you must be pleased you are so far advanced.

Perhaps we ought to modify the old saying by exclaiming, 'What about the Reptiles' because these guys are terrific little workers around the garden and whose object in life is to keep all the pests and insect nasties under control. How could you not like them.

I was wondering if there was any interbreeding between the bobtails and western bluetongues. Although I have only seen a couple of examples over the years (on the Esperance sandplain), they looked to be more heavily banded than a bobtail (or conversely, too roughly skinned to be a skink) and the tail seemed to be somewhere in between.

My Other Blogs

There are three blogs that I manage, so if you find one with no recent posts, please try one of the others. They all deal exclusively with the flora and fauna of the Esperance region of Western Australia, so may also be of interest.

About Me

An ardent nature lover who is happiest when in the bush. The object of this blog is to record the nature around me, particularly the unusual or rarely encountered flora and fauna. My photography is governed by my equipment that being a modest Canon A80 PowerShot Camera with standard lens. So I do not set out to portray subjects in high photographic detail, but to show them in an interesting pose and to highlight species characteristics.